The polls close at 8 p.m. ET. Am I right in thinking that after two months and 26 elections, these are the first primaries that are legit toss-ups between all three candidates? Until now, it’s always been Romney vs. either Santorum or Gingrich as the regionally designated Not Romney, but tonight either state could break for any of them. RCP has them separated by less than three points in Alabama and six points in Mississippi. And bear in mind, per Nate Silver, polls of the deep south have been less reliable in recent years than polls of other regions. Anything could happen here, including a pair of 32/31/30 splits. Excitement.

Jay Cost notes that Romney should have a better shot in Alabama because he does well with urban voters and there are more of them there than in Mississippi. Serious question, though. Is a sweep Mitt’s most desirable outcome tonight? He badly wants to win one of these states so that he can claim the approval of the GOP’s southern base, but if he takes them both, Gingrich will be devastated and might very well quit notwithstanding his tough talk this morning. Romney doesn’t want a two-man race with Santorum: If Team Sweater Vest starts beating him head to head, then Mitt could well end up in June with a plurality of delegates (thanks to proportional rules) but a badly weakened case for why he should be the nominee at a brokered convention. I’m thinking maybe his optimal scenario is to win one state and have Newt win the other. That’ll keep Gingrich in the game while still giving Romney bragging rights about a win in the deep south. By the same token, the Romney (and Gingrich) disaster scenario is Santorum winning both states. It would give RS a killer talking point about the base lining up behind him to be the RINO dragon-slayer, which might be the death blow for Newt.

Here’s the Google Elections page for all your result-following needs. Don’t get too caught up in delegate counts for these states, though — Hawaii and American Samoa are also voting today so the numbers will change as their results come in overnight. (Romney is favored.) Lots of updates coming, including exit polls as soon as they’re available. While we wait, a point to ponder: Are we sure that Gingrich dropping out would be a big problem for Mitt? His own team claims that it wouldn’t. Based on some of the poll data, they might be right.

Update: Preliminary exit poll results show a lots of evangelicals turning out in both states, which is no surprise and is good news for Santorum, needless to say. The proportion of those voters in Alabama and Mississippi are in line with the proportions in Tennessee and Oklahoma, both of which he won comfortably.

Update: As promised, the Alabama and Mississippi exit polls. Back in a few with highlights.

Update: An interesting gender split in Alabama: Newt narrowly won men while Santorum won women by eight points. (So much for the “women hate RS” meme.) And yet, based on the numbers, it looks like Newt is set to finish just a hair behind Romney in third place. Two other interesting data points. First, ideology:

That’s confirmation of the CW all the way. Santorum wins righties over Newt, the center-right splits three ways, and then Romney cleans up with moderates and liberals. Similarly:

Rarely have you seen three different candidates split this perennial question about qualities the electorate is looking for, but here you go. Again, perfect reflection of the CW. See why we’re in for a close race?

Misssissippi exit analysis coming up.

Update: Same odd story for Newt in Mississippi. He wins narrowly among men but may yet end up finishing a very close third because of Romney’s and Santorum’s relative strength with women. Here’s the data point of the night so far, though:

Fully 80 percent of the electorate is evangelical — and Romney somehow managed to fight Santorum to a draw among them. If he ends up winning the state, that’s the story. Another surprisingly strong Romney showing comes with voters without a college degree. That’s supposed to be Newt’s and Rick’s bread and butter, but no:

Romney also tied Santorum for the lead among voters who make less than $50,000 per year. As for qualities in a candidate, Mississippi looks a lot like Alabama:

And one more just for fun that someone flagged on Twitter:

Among voters who said Ron Paul’s positions are “about right,” the candidate of choice is … Mitt Romney?

Needless to say, Santorum can live with splitting these states with Romney. Job one is getting Gingrich out of the race ASAP. If Newt finishes third in both, we might very well see it. I wonder if we’ll see it tonight.

Update: David Freddoso has a copy of a memo sent out tonight by Team Newt vowing that they’ll soldier on, which sounds like they’re conceding the evening. Bachmann vowed to soldier on the night she finished last in Iowa too but was gone the next day. Stay tuned.

Update: It’s now 90 minutes after the polls closed and … 7.2 percent of Alabama precincts have reported. Santorum leads there and in Mississippi (where 24 percent have reported) as I write this.

Update: Romney told CNN earlier that Santorum is at “the desperate end of his campaign.” Right message, wrong target.

Update: At 9:53 ET, and with only 26 percent reporting, NBC finally calls Alabama for Santorum. And don’t look now, but with 78 percent reporting in Mississippi, Santorum is clinging to a 2,000-vote lead over Gingrich. Romney is another 2,000 votes back. Looks like the exits got it wrong there, likely vis-a-vis the evangelical numbers.

The worst-case scenario for Mitt tonight was a Santorum sweep. We’re on the verge of it.

Update: Aha. Philip Klein notes that CNN has now updated their exit poll numbers. (Unfortunately, the early data isn’t always final.) Remember how it was a big deal that Romney and Santorum were tied at 32 among evangelicals in Mississippi? Here’s how it looks now:

That’s why Rick is doing better than expected and Mitt’s doing worse.

Update: Mississippi’s not called yet but Team Santorum is already elbowing Newt:

Rick Santorum spokesperson Alice Stewart said she believes after Tuesday night it will be a “two-man race” between Santorum and Mitt Romney…

A “son of the South” like Gingrich, she said, “should be doing much better than this.”

“This is going to be, after tonight, this will be a two-man race,” Stewart said. “It’s going to be Rick and Mitt, and we’re going to clear the field and Rick’s got a good shot down the road.”

Update: Now 83 percent reporting in Mississippi and the numbers are holding — Santorum by 2,000 votes over Gingrich and Romney 5,000 votes behind. Jackson’s county, where Romney is piling up votes, is 89 percent in right now so there’s not much meat on the bone left there either for him.

Update: With 90 percent in now, Santorum’s lead has expanded to more than 3,000 votes. I’m reluctant to forecast a race even at this late hour after the last-minute Romney comeback in Ohio, but it looks like Team Sweater Vest is going to pull off the sweep. One last dramatic twist to this interminable primary.

Update: More than 96 percent in now as of 10:40 ET and Santorum’s lead is nearly 4,000 votes. He’s going to pull this off and Romney’s going to finish third in both states. What a deflating defeat for the presumptive nominee, especially after that early exit poll had him winning Mississippi. We should get the call soon.

While the idea Gingrich could or would win a brokered convention seems absurd, it is likely that continuing to accrue delegates would give him additional bargaining leverage going into the Republican convention in Tampa this summer.

But there are good reasons for Gingrich to reject that cynical strategy. First, if he truly believes Mitt Romney is a “Massachusetts moderate” masquerading as a conservative, then he owes it to Republican voters to give former Sen. Rick Santorum a clean shot at wresting the nomination from him. I’m pretty sure Santorum has earned it.

Second, staying in the race — merely in order to play a king maker or to curry favor at a later time — is hardly the most honorable or inspiring reason to remain in a race. Gingrich would be essentially asking donors to contribute money to a campaign he knows cannot win — and he would be asking voters to cast their votes for a candidate he knows can’t win.

Gingrich’s problem after tonight is that he might have lost the last shreds of his constituency, whether or not he’s inclined to quit. If you’re a Republican who’s dead set against nominating Romney, what’s the argument for sticking with Newt? Either you’re staying home because you can’t stand Santorum or else you’re gritting your teeth and pulling the lever for the Sweater Vest. There’s no compelling reason to go to the polls for Gingrich. He can’t win even in his own backyard.

Update:PPP: “Our NC GOP poll coming out tomorrow shows an 8 point shift toward Santorum if Newt was out. Nothing but a spoiler at this point.” If Newt wants revenge on Romney for spoiling his chances in Iowa and Florida, dropping out and endorsing Santorum is his best option.

Update: Gingrich is giving his concession speech now and vowing to go on but I don’t think it’s up to him. His voters need to decide their next move. If they break for Santorum and he starts beating Romney head to head — starting next Tuesday in Illinois — then he’s got a compelling narrative headed into the convention even if Mitt ends up winning a plurality of delegates. Namely, “the only reason Romney ended up with a delegate lead is because Newt and I split conservatives in the early primaries. Once Newt faded and it turned into a binary choice, I was the clear preference of the majority.” That is to say, if Santorum can put together a winning streak against Romney, he can point to tonight’s results as a de facto “reset” of the primary. Southern voters discarded Gingrich and adopted him and that propelled him to a series of wins. Forget the delegate count and focus on that strenuous “Not Romney” sentiment among Republican voters. That’s his argument. Romney needs a counter.

Update: Here’s Santorum’s speech, in which he marvels “we did it again.” Elsewhere, Nate Silver remembers that Gingrich’s own spokesman called Alabama and Mississippi must-wins for him just a few days ago.